The invention is directed to a method and apparatus for intelligently stopping a fan motor. Merely by way of example, the invention has been applied to techniques of using a microcontroller to control braking the fan motor whenever a main power supply is on or off. But it would be recognized that the invention has a much broader range of applicability.
In electronic systems, such as computer systems or telecommunication systems, cooling fans are widely used for maintaining system operational capabilities. Because of the complexity of these electronic systems, cooling fans not only need to perform the traditional function of providing cooling air, but also need to have some intelligence in order to provide a user with specialized control of the fan motors. A typical conventional modern fan motor is of a type known as a brushless DC motor. Such a motor includes, among other things, a stator coil coupled to a DC power supply for inductively driving a permanent magnetic rotor in accordance with a commutation signal.
Due to variations in the DC power supply which commonly occur during normal operation of a fan, the speed of the fan will vary. In extreme situations, the power supply may effectively be removed (e.g., failure in the power supply, disconnection of the power supply), resulting in a loss of power to the fan. The fan blades will continue to rotate due to inertia and the inductive energy that is stored in the stator coils. However, when power from the fan is removed intentionally, say for maintenance reasons, the maintenance person will have to wait for the fan blades to spin down before doing any work. For large cooling fans which operate at high speeds, the spin down can take long time.